Call appearance buttons are used to display alerts for incoming calls directed to a user’s extension number or to a hunt group of which they are a member. Call appearance buttons are also used to make outgoing calls.
By having several call appearance buttons, a user is able to be alerted about several calls, select which call to answer, switch between calls and take other actions.
When all the user’s call appearance buttons are in use or alerting, any further calls to their extension number receive busy treatment. Instead of busy tone, the user’s forward on busy is used if enabled or otherwise voicemail if available.
Call appearance buttons are the primary feature of key and lamp operation. None of the other appearance button features can be used until a user has some call appearance button programmed.
There are also addition requirements to programming call appearance buttons:
Call appearance buttons must be the first button programmed for the user.
Programming a single call appearance button for a user is not supported. The normal default is 3 call appearances per user except on phones where only two physical buttons are available.
 For Release 4.2+, T3 phones support the use of Line Appearance buttons. These can be programmed against buttons on T3 phones without requiring call appearance buttons. See T3 Phone Line Appearances.